There is a complex network of collagen fibrils in the heart. While the precise function of the various components of this network are not clearly defined, it may act to direct the force developed by sarcomeres to the ventricular cavity and transmit the diastolic filling pressure to the myocytes up to the point at which adjacent cells are near the same length. This collagen matrix in the heart is markedly altered in a variety of disease states. However, the mechanism through which the collagen matrix is altered, and the morphology and mechanical consequences of the altered matrix have not been classified. This proposal will examine the biochemical mechanisms, morphological alterations, and mechanical consequences of alterations in the cardiac collagen matrix using two models of collagen dissolution. In the first, we will perfuse rat hearts in vitro or dog hearts in vivo with oxidized glutathione or 5, 5'- Dithio-bis (2 nitrobenzoic) acid (DTNB) to effect removal of tissue collagen. We have determined that oxidized sulfhydryl reagents can induce a collagenolytic activity in these cardiac preparations. Since oxidized glutathione is produce and possibly released by ischemic myocytes, we will determine if oxidized sulfhydryl reagents is the operant mechanism for the expression of collagenolytic activities observed in ischemic tissue. Thee models will enable us to examine in a controlled, non-ischemic tissue the mechanical consequences of collagen removal from cardiac tissue and analyze the collagen peptide products obtained following induction of collagenolytic activity. Chronic in vivo canine experiments will also allow us to define the time course and nature of the collagen types found during tissue replacement of collagen in the area perfused by oxidized sulfhydryls. It is not know at the present time if collagen removal alone (i.e. non- ischemic) will result in collagen replacement of a similar protein pattern and concentration when compared to ischemic tissue. The second model involves the hearts response to a single injection of 6 mg/kg of adriamycin in rats. Following 3-4 weeks after injection, collagen loss becomes markedly apparent using scanning electron microscopy. This model will afford another, approach to investigate the mechanism and extent of cardiac collagen loss, its mechanical consequences and the dynamics and character of collagen replacement.